The Fourth Generation (4G) communication system enabling the high-speed transmission of large-scale data uses an Orthogonal Frequency Division Multiplexing (OFDM) scheme or an Orthogonal Frequency Division Multiplexing Access (OFDMA) scheme. The OFDM scheme or the OFDMA scheme divides a bandwidth into a plurality of subcarriers to transmit data, and specifically, converts a serially input data row into N number of parallel data rows (where N is a natural number equal to or more than two) and carries the parallel data rows in the respective divided subcarriers, thereby increasing a data rate.
To enhance the efficiency of data transmission, a communication system using the OFDM scheme or the OFDMA scheme uses a Multi-Input Multi-Out (MIMO) scheme in which a base station including a plurality of antennas transmits different data through the respective antennas. By using the MIMO scheme, the communication system can obtain a diversity gain and moreover increase a data transmission rate.
Especially, by using the MIMO scheme, data or signals are simultaneously transmitted and received between a base station and a plurality of mobile stations. In such a Multi-User (MU) MIMO scheme, M number of antennas (where M is a natural number equal to or more than two) are arranged in a base station, and N number of antennas are arranged in a plurality of mobile stations. In this way, signals are respectively transmitted and received through the arranged antennas, thereby increasing a transmission rate.
As described above, a precoding technique may be applied to the MU-MIMO scheme, for minimizing inter-user interference and maximizing the sum rate.
Here, precoding is a type of techniques for enhancing the reliability of data transmission in a wireless communication system, and denotes a technique that generates a precoding matrix on the basis of information on fading and interference which occur in a channel in transmitting data, precodes data to be transmitted with the precoding matrix, and transmits the precoded data, thereby enhancing the reliability of data transmission.
However, since the 4G mobile communication system uses codebook having a limited size and reports channel information in the forms of Channel Quality Indicator (CQI), Rank Indicator (RI), and Precoding Matrix Indicator (PMI) at present, available precoding matrixes are limited, and thus, there are limitations in reducing inter-user interference and increasing the sum rate.